The invention relates to toothed belts and sprockets but more particularly, the invention relates to belts with curvilinear fore and aft flank surfaces and sprockets for use therewith.
Toothed belts are extensively used in synchronous drives as substitutes for chain drives or gears. Unlike chains and gears that have pitch circles intersecting a gear or sprocket tooth, belt drives have a pitch line displaced from the belt and sprocket teeth and substantially located at the belt tensile member. The displaced pitch line introduces a problem of assuring good entry of a belt tooth into a belt sprocket cavity with a minimum of interference at various belt loads and sprocket diameters. The belt tooth/sprocket interference problem is compounded by belt pitch changes caused by elongation of the belt tensile member; deflection of elastomeric belt teeth; and chordal spanning of the belt tensile member at or between sprocket teeth under load. A trend in solving some of the belt tooth/sprocket fit problems under various loadings, is to go from the traditional belt tooth that has a trapezoidal cross section, to a belt tooth having fore and aft flank surfaces shaped with arcs having centers substantially confined within a belt cross section encompassing each belt tooth. Examples of belts with teeth having curvilinear fore and aft flank surfaces are taught in U.S. Pat. Nos.: 3,756,091 to Miller; 3,977,265 to Worley et al.; 3,924,481 to Gregg 4,108,011 to Gregg et al. While such belts have teeth that roll or slide into engagement with a sprocket, their design may require the fore and aft flank surfaces to form angles greater than 15 degrees with a normal to the belt tensile member; introduce belt tooth interference with a sprocket at various belt loads; or prevent the belt teeth from being of maximum possible cross section to minimize tooth deflection or impair belt ratcheting. The object of the present invention is to overcome the deficiencies of such belts.